Gas tank venting

[Davidej M]

The fuel tank in my 1992 Winnebago has a partial vacuum created as fuel is consumed which is relieved when I remove the filler cap during filling to the extent that the tank rebounds (boing!!!) when the filler cap in removed.
I can't believe this is good for the tank in the long term as the metal will eventually fatigue at the point of stress. The Ford manual talks about having the correct filler cap as the ventilation is through the cap. The cap appears to be the original equipment.
Does anyone have any comments?

[Davidej M]

The fuel tank in my 1992 Winnebago has a partial vacuum created as fuel is consumed which is relieved when I remove the filler cap during filling to the extent that the tank rebounds (boing!!!) when the filler cap in removed.
I can't believe this is good for the tank in the long term as the metal will eventually fatigue at the point of stress. The Ford manual talks about having the correct filler cap as the ventilation is through the cap. The cap appears to be the original equipment.
Does anyone have any comments?

[Ray,IN]

For the low price involved, just buy a new one for your make/model chassis. That condition is not right. If anything, the tank should be slightly pressurized from the action of containing fumes, as required by EPA standards.